Recovery of mixed plating rinses

ABSTRACT

A METHOD AND SYSTEM FOR TREATING MIXED RINSE WATERS USED TO RINSE WORKPIECES REMOVED FROM CHROMIUM AND OTHER METAL TREATING BATHS PROVIDES FOR REDUCING HEXAVALENT CHROMIUM IONS CARRIED BY THE WORKPIECES PRIOR TO RINSING AND MIXING THE RINSE WATERS FROM A PLURALITY OF DIFFERENT RINSES PRIOR TO PASSAGE THEREOF THROUGH CATION   AND ANION EXCHANGERS. THE METHOD AND SYSTEM ALSO PROVIDE FOR THE IMMEDIATE REMOVAL OF CN FROM THE ANION REGENERANT WHILE IT HAS A HIGH PH VALUE AND THEN COMBINING THE CATION AND ANION REGENERANTS PRIOR TO NETRALIZATION.

g- 1, 1972 J. F. ZIEVERS ETAL RECOVERY OF MIXED PLATING RINSES FiledApril 8, 1971 0 3 2 9 00 N0 720 6 002E 002.0 062;. :20 v60; 02350 52;730 6. 522 E0 52; @2530 E 0000 0500 5 0000 06 0 60 50000 5E; 0m 0 0wN zow0 :50 02.2 5 06 g 2. mm mm 3 .50 :20 002E 002E 0622 V2: 025 5 0050 6;00.2; 002; 00.5; :20 .50 20.20010 52; S: 0 60 0 60 0260000 300 0 60 a 4x 0 0 m; 0057650 00 52050 United States Patent 3,681,210 RECOVERY OFMIXED PLATING RINSES James F. Zievers, La Grange, and Charles J.Novotny, Hickory Hills, 111., assiguors to Industrial Filter & Pump Mfg.Co., Cicero, Ill.

Filed Apr. 8, 1971, Ser. No. 132,416 Int. Cl. Billj 1/04; C021 1/42,1/60 US. Cl. 204-35 R Claims ABSTRACT OF THE DISCLOSURE The presentinvention relates to a new and improved method and system forsimultaneously treating toxic water resulting from the rinsing ofworkpieces carrying diflerent metal plating solutions, and it relatesmore particularly to a method and system for recovering water used torinse workpieces in a metal plating or treating line carrying, forexample, solution containing chromium and cyanide ions.

The common practice in the metal plating industry is to remove the metalplating solution carried by the workpieces from the plating bath byrinsing, spraying, or washing the workpieces with water. Not only doesthis water become toxic, thereby necessitating treatment before itsdisposal, but it also contains sufficient quantities of the platingmetal as to make the treatment economical if such metal is recovered.

Generally speaking, two or more difierent metals will be sequentiallyplated on the same workpiece in a single plating line, and in some casesseveral different plating lines are operated in the same generallocation or at least at the same plant. In order to minimize the cost ofoperating such plating lines and to insure that no toxicity is releasedfrom the rinse water, it would be desirable to provide a completelyclosed rinse water system. Such a system would have the added advantageof minimizing the use of water which is consumed in extremely largequantities in plating systems of the prior art. It would be furtherdesirable to provide a system wherein all of the rinse water from eachmetal plating line including the acid dip and alkaline cleaning stationsas well as the water from several plating lines could be mixed andsimultaneously deionized prior to recirculation to the various rinsingstations.

An object of the present invention is, therefore, to provide a new andimproved method and system for recovering rinse water used in metalplating systems.

Another object of the present invention is to provide a new and improvedsystem for recovering the water used to rinse workpieces removed from achromium plating solution.

A further object of the present invention is to provide a new andimproved system for recovering water used to rinse workpieces carryingvarious metal plating solutions.

A still further object of the present invention is to provide a new andimproved method and system for simultaneously deionizing the rinse waterused for removing dilferent metal plating solutions from workpieces.

3,681,210 Patented Aug. 1, 1972 Briefly, the above and further objectsof the present invention may be realized by moving the workpieces from achromium plating solution directly into a reducing bath prior torinsing, thereby to convert the hexavalent chromium ions carried by theworkpieces to trivalent chromium ions. The workpieces are then movedthrough water rinse baths or sprays wherein the liquid carried by theworkpieces is transferred to the water. Inasmuch as the rinse water doesnot contain any hexavalent chromium, it may then be mixed or combineddirectly with the rinse water from other metal plating stations such,for example, as nickel plating, copper plating, or zinc plating stationsand the mixed waters subjected to the usual deionization treatment bypassing them sequentially through cation and anion exchange resincolumns.

Further objects and advantages and a better understanding of the presentinvention may be had from the following detailed description taken inconnection with the accompanying drawing which is a schematic flowdiagram of a typical chrome plating line as used, for example, inplating automobile bumpers.

Referring now to the drawing, there is shown a chrome plating linecomprising a plurality of adjacent tanks generally arranged in the shapeof a horseshoe with the work traveling in a clockwise direction as it iscarried from one tank to the next in the system. As will be understoodby those skilled in the art, the exact arrangement of the varioussolutions through which workpieces are moved during a plating operationis subject to substantial variation, and therefore, the plating lineshown in the drawing is merely by way of illustration of a typical typesystem with which the present invention finds application.

As shown, the workpieces are first immersed in an alkaline cleaning bath10 and then rinsed in a cold water rinse tank 12 before moving into anelectrolytic cleaning bath 14. The workpieces are again cleaned in acold water rinse tank 16 and lightly dipped in an acid bath 18 beforeagain being washed in a cold water rinse tank 20. The parts are thenelectro-plated with copper while immersed in a copper plating solutionin the tank 22. Typically, this solution will contain Cu(CN) KCN, andKOH. After removal from the copper plating bath tank 22, the workpiecesare washed in a cold water rinse tank 25 and again in a second coldwater rinse tank 26. In accordance with common plating practices, thefresh water enters the cold 'water rinse tank 26 and flows over a weirbetween the tanks 24 and 26 into the tank 24 and flows out of the tank24 at the same rate as water enters the tank 26. The workpieces are thenimmersed in a nickel plating solution contained in a tank 28 wherein alayer of nickel is electroplated over the copper layer previously platedonto the workpieces. The nickel plating bath will typically contain Ni,NiCl boric acid, sodium formate, cobalt formate, formaldehyde andbrighteners.

After being plated with the desired thickness of nickel, the workpiecesare moved from the bath 28 into a first cold water rinse tank 30, theninto a second cold water rinse tank 32 and into a third cold water rinsetank 34. As shown, fresh water enters the rinse tank 34 and flows oversuitable weirs first into the tank 32 and then into the tank 30 fromwhich it exits at a rate equal to the rate at which water enters thethird tank 34.

After being thus thoroughly washed, the nickel plated workpieces are nowimmersed in a chromium plating solution contained in the tank 36 whereina layer of chromium is electroplated thereon over the nickel. Thechromium plating solution typically includes H CrO and H This solutionwill contain a substantial number of hexavalent chromium ions as well asa substantial number of trivalent chromium ions which are generatedduring the plating operation. The workpieces after leaving the chromiumplating tank 36 are immersed in a drag-out bath contained in a tank 38.The solution in the tank 38 is essentially the same as the solution inthe tank 36 although at a substantially lower concentration.Accordingly, the tanks 36 and 38 both contain the chromium platingsolution including both hexavalent and trivalent chromium 1011s.

In accordance with an important feature of the present invention theworkpieces leaving the chromium plating solution contained in the tank38 are immediately immersed in a reducing solution contained in the tank40. The reducing agent may, for example, be NaHSO' and its purpose is toreduce or convert the hexavalent chromium ions to trivalent chromiumions before the workpieces are washed. When the workpieces are removedfrom the tank 40, they move through a pair of cold water rinse tanks 42and 44 wherein the solution carried by the workpieces is substantiallycompletely washed therefrom. As shown, fresh water is supplied to thetank 44 and passes over a weir into the tank 42 before exiting at a ratesubstantially equal to the rate at which fresh water enters the tank 44.After leaving the tank 44, the workpieces may be immersed in a hot waterrinse contained in the tank 46 to minimize dry out time.

In accordance with the present invention, the rinse waters from therinse tanks 42, 30 and 24 are combined or mixed and supplied via a line50 to a cation exchange column 52 containing a cation exchange resinwhich removes the trivalent chromium ions and any other cationscontained in the rinse water. For example, in the system illustrated anddescribed above, sodium ions Will also be removed from the rinse waterby the cation exchange resin in the tank 52. The solution then passesthrough a line 54 to an anion exchange column 56 containing an anionexchange resin. The various anions contained in the solution are removedby the anion exchange resin in the column 56 and completely deionizedwater flows out of the column 56 from which it is recirculated to thevarious cold water rinse tanks 26, 34 and 44. It will be realized bythose skilled in the art that it is not necessary to utilize deionizedwater for rinsing the workpieces after the copper plating and nickelplating operations. Nevertheless, with the present invention it iseconomically possible to use deionized water at all rinse stations inthe plating system, thereby providing better washing than has beenachieved with the prior art. Any make up water to be added to replacethat water which has evaporated may be added just prior to the cationexchange resin or if desired it can be added at either the tank 26 orthe tank 34.

The cation exchange resin in the column 52 will be regenerated bypassing an acid such, for example, as H 80 therethrough and the anionexchange resin will be regenerated by passing a hydroxide such as NaOHtherethrough. 'Ihe regeneration solution coming oif the cation exchangeresin will thus contain Na SO Cr (SO at a low value of pH e.g.approximately 3. The regenerant coming off the anion exchange resin willcontain NaCN, NaCl, at a pH of approximately 10. This latter regenerantmay be immediately treated with chlorine while at the high pH value toremove the CN ions and then blended directly with the regenerant fromthe cation exchange resin prior to the addition of an acid or alkali toneutralize the combined regenerant solutions. Accordingly, the expenseof repeatedly altering the pH level of the regenerant solutions in orderto remove the cyanide ions from the anion exchange resin and then toremove the hexavalent chromium ions therefrom is obviated with thepresent system.

The process of the invention is illustrated in greater detail in theexamples set forth below. It is to be understood however, that theexamples are illustrative only and that the proportions of reagents, thespecific acids, bases and salts employed therein can be changed withinthe racked workpieces such as automobile bumpers is passed through acopper plating bath containing 8 oz. per gal. of copper cyanide, from0.75 to 1.5 oz. per gal. of potassium cyanide and from 4 to 7 oz. pergal. of potassium hydroxide. Generally, it will be necessary to cleanthe workpieces in a preliminary plating preparation process utilizingconventional treatment tanks providing alkaline cleaning, electrolyticcleaning, acid cleaning and appropriate cold water rinses.

After the work line leaves the copper plating bath, the workpieces arerinsed in cold water and then passed into an electroplating bathcontaining from 9 to 10 oz. per gal. of metallic nickel, 7 oz. per gal.of nickel chloride, 4.75 oz. per gal. of boric acid, 5.6 oz. per gal. ofsodium formate and 2.5 oz. per gal, of cobalt formate. Thereafter, thenickel plated workpieces are thoroughly rinsed with cold water andimmersed in a chrome plating solution containing 33 oz. per gal. ofchromic acid (H CrO and 0.33 oz. per gal. of sulfuric acid.

The workpieces upon leaving the chrome plating bath carry out asubstantial quantity of chromium solution containing hexavalent chromiumions as well as trivalent chromium ions generated during the platingoperation. Therefore, in this example a drag out bath is employed toreduce the concentration of Cr and Cr ions in the solution carried bythe plated workpieces as they leave the chromium plating station. Bythis method, the concentration of chromic acid in the carried outsolution will value from zero to about approximately three percent byweight.

The workpieces are immediately immersed in a reducing solution of sodiumbisulfite (NaHSO at a pH of approximately 2.0-3.0 wherein all chromiumpresent as Cr ions is reduced and converted to Cr+ ions. The solutioncontaining trivalent chromium ions carried by the workpieces from thereducing bath is washed from them in a cold water rinse tank and therinse water mixed with the rinse water from the previous rinsesfollowing the copper and nickel plating steps, is recovered by passingit across the surfaces of a cation exchange resin and then across thesurfaces of an anion exchange resin.

As has already been mentioned above, in accordance with the presentinvention, waste water from one or more other plating lines can be mixedwith the waste water from the copper-nickel-chromium work process lineof the above example and simultaneously deionized prior to recirculationto the various rinsing stations. For example, the waste water from azinc plating station can be combined with the waste water coming fromthe coppernickel-chromium plating line. In this example the zinc platingbath contains 8 oz. per gal. of zinc cyanide, 5.6 oz. per gal. of sodiumcyanide, 10.5 oz. of caustic soda and 4.5 oz. per gal. of metallic zinc.Rinse water from workpieces coming from the zinc plating bath is thenmixed with the rinse water from the copper, nickel and chrome platingsteps and simultaneously recovered by passing the combined rinse watersacross the surfaces of a cation exchange resin and then across thesurfaces of an anion exchange resin.

From the above it will be readily seen that by moving the workpiecesdirectly from a chromium plating bath into a tank containing a strongreducing agent, all chromium ions entering the rinse recirculationsystem have been converted to the trivalent state and therefore all suchions are removed from the rinse water on the cation resin of a rinserecirculating demineralizer station. Accordingly, by this process, thepossibility of the presence of hexavalent chromium on an anion resin andthe expensive anion regenerant effluent treatment problem attendantthereto, can be completely eliminated.

While the present invention has been described in connection withparticular embodiments thereof, it will be understood that many changesand modifications of this invention may be made by those skilled in theart without departing from the true spirit and the scope thereof.Accordingly, the appended claims are intended to cover all such changesand modifications as fall within the true spirit and scope of thepresent invention.

What is claimed is: 1. A method of recovering water used in a chromiumplating system, comprising the steps of moving the workpieces directlyfrom a chromium plating solution containing hexavalent chromium into areducing bath wherein hexavalent chromium carried by the workpieces fromthe plating solution is converted to trivalent chromium, then rinsingsaid workpieces in water, flowing the water in which said workpieceshave been rinsed across the surface of a cation exchange resin to removethe trivalent chromium ions therefrom,

then flowing the efiluent from said cation exchange resin through ananion exchange resin to remove anions therefrom to provide an effluentof substantially purified water, and

recirculating said purified water to rinse said workpieces.

2. A method according to claim 1 comprising the additional steps ofregenerating said cation exchange resin by passing an acid regenerantacross the surfaces thereof,

regenerating said anion exchange resin by passing a hydroxide regenerantacross the surfaces thereof, treating the regenerant passed across saidanion exchange resin to remove the cyanide ions therefrom while saidregenerant has a high pH value, then blending said treated regenerantwith the regenerant passed across said cation resin, and

neutralizing said blended regenerants.

3. A method according to claim 2 wherein said step of treating theregenerant from the anion exchange resin is carried out by addingchlorine to said regenerant.

4. A method according to claim 3 wherein said chlorine is added to saidregenerant while said regenerant has a pH value of about ten.

5. A method of recovering rinse water used in a metal plating systemwhich includes a chromium plating bath and at least one other metalplating bath, comprising the steps of moving the workpieces directlyfrom the chromium plating bath into a reducing bath wherein hexavalentchromium carried by the workpieces is converted to trivalent chromium,then rinsing said workpieces in deionized water, combining said water inwhich said workpieces have been rinsed with the water in whichworkpieces removed from said other plating bath have been rinsed,

passing the combined rinse waters through cation and anion exchangeresin beds, and

then recirculating the water to rinse workpieces being plated in saidsystem. 6. A method according to claim wherein said other metal platingbath contains nickel ions. 5 7. A method according to claim 5 whereinsaid other metal plating bath contains copper ions. 8. A methodaccording to claim 5 wherein said other metal plating bath contains zincions. 9. A method of recovering rinse water used in a plat- 10 ingsystem wherein workpieces are immersed in nickel and chromium platingbaths, comprising the steps of moving workpieces from a nickel platingbath into a running water rinse bath, moving workpieces from a chromeplating bath directly into a reducing bath wherein hexa-valent chromecarried by the workpieces is converted to trivalent chrome, then rinsingthe chrome plated workpieces in a running water bath, combining thewater from both said rinse baths and passing it first across the surfaceof a cation exchange resin and then across the surface of an anionexchange resin, and reusing said water to rinse said workpieces. 10. Amethod according to claim 9 further comprising the steps of immersingsaid workpieces in a copper plating bath and then rinsing saidworkpieces in a running water bath before immersing said workpieces insaid nickel plating bath; and combining the water in which saidworkpieces have been rinsed prior to immersion thereof in said nickelplating bath with the water from the other of said rinse baths prior topassing said water across said resins.

References Cited UNITED STATES PATENTS 1/ 1956 Costa 2110-38 X 12/ 1968Yagishita 21037 X 11/19'70 Yagishita 204-237 X 1/1971 Buchanan 204-35 RX OTHER REFERENCES GERALD L. KAPLAN, Primary Examiner US. 01. X.R.

117-102 A; 204-45 R, 49, 51, 1 R, 52 Y, 55 Y, 232, 237; 21037, 38

